Function of parathyroid glands in kidney transplant patients--diagnostic value of CAP and CIP

As shown in the last four years, Nichols assay for the estimation of "intact" parathyroid hormone (i-PTH) apparently overestimates parathyroid gland function by recognizing both the whole PTH- 1-84 molecule (identified as a cyclase activating PTH - CAP) and N-truncated fragments of PTH-7-84 (identified as a cyclase inactive PTH - CIP). As PTH-1-84 and PTH-7-84 are presumed to show antagonistic effects on calcaemia and bone turnover, we aimed to assess the relationship between PTH-1-84 and PTH-7-84 plasma levels respectively and bone turnover markers in kidney transplant patients.

52 patients and 17 healthy subjects were examined at least 4 years after renal transplantation. In all subjects the following parameters were assessed: bone mineral density (BMD) of the total body, L2-L4 vertebrae and femoral neck (DEXA), serum total PTH (i-PTH) and PTH-1-84 level, as well as the difference between total PTH and PTH-1-84 (reported as PTH-7-84), activity of alkaline phosphatase (AP), serum concentration of collagen type I cross-linked C-telopeptide, osteocalcin (OC), creatinine (creat), 25-OH-D, total calcium (Ca(total)) and phosphorus (P) concentration.

Tx patients were characterized by significantly elevated plasma values of all examined parameters except activity of AP and plasma level of Ca, P and 25-OH-D. Both in HS and Tx patients a significant positive correlation was found between plasma concentration of PTH-1-84 and PTH-7-84. In addition in Tx patients both PTH-1-84 and PTH-7-84 showed a significant positive correlation with plasma creatinine, OC, AP and Ctx and a negative one with BMD T score, while in HS PTH-1-84 and PTH-7-84 were positively correlated with OC and AP and negatively with Ca and BMD (borderline significance).

Presence of highly significant correlations between PTH-1-84 or PTH-7-84 and markers of both osteogenesis and osteolysis respectively is not consistent with a diagnostic superiority of PTH- 1-84 and PTH-7-84 over total PTH estimation in patients 4 or more years after renal transplantation.